Photoelectric amplifying system



June 2,

1936. A KAROLUS 2,042,602

PHO TOELECTRIC AMPLIFYING SYSTEM Filed Jan 27, 1930 INVENTOR AUGUST KAROLUS ATTORNEY Patented June 2, 1936 UNITED STATES PATEN OFFICE August Karolus, Leipzig, Germany, assignor to Radio Corporation of America, a corporation of Delaware Application January 27, 1930, Serial No. 423,592

In G

15 Claims.

This invention is concerned with the spotting (spot-photography) of pictures for transmission, particularly for television purposes. On account of the wide frequency bands occurring in this case, it is necessary to generate. a carrier frequency which is photoelectrically modulated by the variations of light and darkness of the picture. In the prior art such a carrier frequency could, for instance, be generated by introducing an alternating voltage into the photo-cell circuit or into the amplifying cascade. This method, however, involved the undesirable feature that, due to the high frequency of the alternating voltage, a steady capacity current was made to fiow in the existing capacities, for instance, between the electrodes of the photo cell. This current might be a multiple of the photoelectric discharge current and its compensation was likely to be impracticable.

The present invention, therefore, provides another method differing from the previous one in that it proposes to insert a resistance or the equivalent, variable with the radio frequency, into the circuit of the picture-spotting photocell. Unlike the introduction of an alternating voltage, this resistance has the eifect of an interrupter which conducts current only as long as the picture-spotting photo-cell is exposed to light. It is not necessary, however, that the interruption of the photo-electric current be complete.

An additional advantage offered by this invention consists in the fact that it is not necessary to interrupt the path of the spotting light itself, 35 which would be particularly objectionable in television on account of the difficulties encountered in conducting and utilizing the light.

Other objects and advantages will at once suggest themselves and become apparent from a consideration of the following specification and claims in connection with the accompanying drawing, wherein:

Fig. 1 illustrates one form of my invention utilizing a second photoelectric element to produce a carrier or tone frequency; and,

Fig. 2 illustrates a modification of Fig. 1, wherein a screen grid tube is used to control the carrier or tone frequency produced in the. spotting photo-cell circuit.

The radio frequency interrupter or current Weakener in the circuit of the spotting or analyzing photo-cell may consist, for example, of a second photo-cell in series with the first and exposed to the action of a controllable light oscillating at high frequency. To achieve this a roermany February 19, 1929 tating perforated disk, for example, a disk such as that shown by Ranger Patent No. 1,789,687, granted January 20, 1931, may be used whose arrangement results in a much simpler construction than that obtainable with the interruption andre-introduction of the spotting light, moving in space. It is, however, possible to eifect the interruption of the light acting upon the second photo cell in a different manner, for instance by inserting a Kerr cell (that is, a Kerr optical system) into the path of the rays of a permanently burning lamp and supplying the electrodes of the Kerr cell with a high frequency potential to control the light striking the photo cell by making use of the electric double refraction phenomenon taking place with the operation of the Kerr cell, as was shown by my prior Pat-' ent No. 1,730,772, granted October 8, 1929. This arrangement may be replaced by a third one, utilizing a piezo-electric oscillating crystal in a known manner for the high frequency control of light and darkness of the polarized light, making use of the double refraction occurring in this case as has been suggested by Hartley in United States Patent No. 1,565,566, granted December 15, 1925. The problem may also be solved in a simple manner with the aid of a gas-discharge lamp, for instance of a cathode glow-discharge lamp, supplied at high frequency. Each of these systems, while not specifically forming a part of my invention, should nevertheless be considered as broadly covering a light interrupting element such as has been generically illustrated by Fig. 1, for example, by the glow discharge device.

The above described embodiment of the invention is diagrammatically illustrated by Fig. 1, wherein l is the picture-spotting photo cell upon which the light, as controlled in intensity by the scanned subject 25, such'as a television subject, a picture or other message for transmission, or a motion picture film, with or without a sound record, not shown, is assumed to fall in direction of the arrow 4, as distributed by any desired form of scanning element such, for example, as the rotary scanning disk 26 to which light is directed from the subject by way of any appropriate optical system 21. The numeral 2 represents the positive (or anode) electrode of the photo-cell, While numeral 3 represents the negative (or cathode) photoelectrically sensitive electrode of the cell, consisting, for instance, of hydrated potassium. The circuit of battery 9 and resistance 8 contains, in addition to cell I, a second photo-cell 5 serving as an interrupter or current weakener and provided with a posi-' tive electrode 6 and a negative electrode 1. The photo-cell circuit is connected to the amplifying tube II by way of the resistance 8. Battery l6 serves to properly adjust the working point on the amplifier characteristic by maintaining a proper bias potential on the grid electrode. thereof. The plate reactance may be supplied by the choke coil l2 whose terminal voltage is transmitted to the next amplifying stage. A plate battery 13 of suitable potential is supplied for the amplifier I I.

According to the invention, the photo-cell 5 is now subjected to radio or high'frequency light oscillations. In the present case these are produced by a glow-dischargelamp l4 provided with an anode l5 and a cathode, l6 located opposite the photo-cell. If the lamp [4 is supplied with alternating current of a high frequency the light emitted by the cathode l6 will oscillate at the same frequency, varying the current-transmitting capacity of cell 5, which thus interrupts or weakens, at high frequency, the photoelectric current which fiows in the spotting or scanning cell I. With a further amplification this frequency is made to-serve as a carrier frequency of'the picture modulation. When a potassiumphoto-cell is used as an interrupting cell 5, it is advisable to fill the glow-discharge lamp I 4 with gases which emitea cathode light of a strongly pronounce-d bluish shade, for instance with nitrogen or argon-nitrogen compounds. With potassium the action of such light is particularly strong so that the glow lamp i4 may be operated with comparatively feeble currents.

Instead of the second light-controlled photocell an electrically controlled thermionic tube may be used as a current interrupter or weakener, either a three-electrode tube or a four-electrode tube of familiar construction with a control grid, or a magnetron tube. In the first case the radio frequency interruption is effected with the aid of a radio frequency voltage appliedbetween the control grid and the filament of the tube which is in series with the spotting photo-cell. of advantage, in view of the introduction of radio frequency alternating voltage, to. apply, in these cases of electrical control of the interruption, a tube with a screening grid, on account of the low harmful electrode capacity of the latter. A circuit arrangement in which such a protectivegrid is employed, and which in addition provides for the compensation of the remaining interfering or disturbing capacity by neutrodyning or neutralizing, is shown diagrammatically by Fig. 2. Herein 5 again represents the spotting photo-cell with the electrodes 2 and 3, the arrow 4 indicating the direction of light modulated by the picture, or other appropriate type of message as above disclosed. Instead of the photo cell 5 shown in Fig. 1, a tube l4 equipped with a screeninggrid is used in this case. The plate voltage is divided into two components or parts It and I! in such a manner as to provide the screening grid I5 with the proper voltage from a point between the battery portions l6 and IT. The controlling grid is is excited with a radio frequency potential from the generator 19 by way of a transformer. The secondary winding of this transformer is tapped to supply the filament, one terminal 20 is connected to the controlling grid 18, the otherterminal 2! to the lead of electrode 2 in the photo-cell by way of an adjustable neutralizing condenser 22. Such a circuit arrangement results, as ,known, in the neutralization of the interfering capacity that still exists It is,

on account of the series connection of the capacities between controlling grid and plate of the double screen tube, on the one hand, and between the electrodes of photo cell I, on the other hand. The photoelectric current which is interrupted or weakened by the radio frequency control of the transmissibility of tube l4 delivers at the terminals of the coupling resistance 8 a radio frequency voltage whose amplitude is controlled by the picture. This voltage is amplified .in a manner identical to that shown by Fig. 1.

The tube M itself does not serve as an amplifier but merely as an interrupter, an attenuator or modifier of the current.

By the above description only two of the many forms which the invention may assume have been described in detail, but it should be borne in mind that the invention is capable of many and various forms, such as are herein suggested and other forms such as naturally follow. Therefore, I believe myself to be entitled to any and all modifications such as fall fairly within the spirit and scope of the following claims, wherein:

I claim:

1. In a system for amplifying currents produced in accordance. with varying intensities of light and shadow influencing a light translating element, a light translating element responsive to varying intensities of light and shadow, a second light responsive device connected in series with said first light responsive element, and means to control cyclically the output from the second light responsive device for interrupting the output from the first light responsive element at a predetermined cyclic rate.

2. A system for converting varying intensities of light and shadow on a record subject to be reproduced into electric current impulses which includes a light responsive element for converting said varying intensities of light and shadow into proportionate strength electric current impulses, and a second light responsive element in series with. said first named element, and means for interrupting the current flow through said second element at a predetermined rate.

3. A system for converting varyinglintensities of light and shadow ona record subject to be reproduced into electric current impulses which includes a light responsive element for converting said varying intensities of light and shadow into proportionate strength electric current impulses, a second light responsive element connected in series with the first light responsive element,

and glow discharge means for interrupting the 7 current flowing through the series combination at a predetermined rate.

4. In a system for converting varying intensities of light and shadow into corresponding and proportionate changes in electrical energy which includes a photoelectric element for converting the said varying intensities of light and shadow into electrical energy, a second photoelectric element in series with said first named photoelectric element, means for supplying light to said second photoelectric element at a predetermined interrupted rate for producing the effect of a chopper frequency on the light reaching said first named photoelectric element, and an amplifying means coordinated with both of said photoelectric elements for amplifying the electrical energy varied in proportion to the intensity of light and shadow on the record subject and interrupted at the rate of interruption of the light to said second named photoelectric element.

5. In an amplifying system, a light responsive element for converting varying intensities of light and shadow into proportionate strength electric current impulses, a second light responsive element connected in series with the first light responsive element, and means cooperating with the second light responsive element for controlling the output energy from the system and alternately causing current to flow and causing current to be interrupted in its passage therethrough so as to produce the effect of a carrier frequency output which is modulated by the light reaching the first light responsive element.

6. In a photoelectric amplifying system, alight responsive element for converting varying light intensities into proportionate strength electric current impulses, a second light translating element connected in series with the first light translating element, alternating current actuated means cooperating with the second light translating element for alternately passing and interrupting current therethrough for producing a chopper frequency in the output of the first light translating element, and means connected with the series connected light translating elements for amplifying the light modulated chopper frequency.

'7. A translating system comprising a pair of serially connected space discharge devices for jointly controlling the current flowing through the system, and means for subjecting each device independently to fluctuating light intensities to vary in accordance With the independent fluctuations both the amplitude and frequency of the output current.

8. An amplifying system comprising a thermionic tube, a plurality of series connected light sensitive elements forming a portion of the input circuit of said thermionic tube, and means for influencing said elements independently by variable intensity light and by constant intensity interrupted light to vary proportionately both the amplitude and the periodicity of the signals appearing in the output circuit of the thermionic tube.

9. An amplifying system comprising a thermionic tube, a plurality of series connected light sensitive elements forming a portion of the input circuit of said thermionic tube, and means for influencing said elements independently by continuous variable intensity light and by constant intensity interrupted light to vary proportionately both the amplitude and the periodicity of the signals appearing in the output circuit of the thermionic tube.

10. An amplifying system comprising a thermionic tube, a plurality of series connected light sensitive elements forming a portion of the input circuit of said thermionic tube, and means for influencing said elements independently by uninterrupted variable intensity light and by constant intensity interrupted light to vary proportionately both the amplitude and the periodicity of the signals appearing in the output circuit of the thermionic tube.

11. An amplifying system comprising a thermionic tube, a plurality of series connected light sensitive elements forming a portion of the input circuit of said thermionic tube, and means for influencing said elements independently by variable intensity light and by constant intensity interrupted light, so that the frequency of the signals appearing in the output circuit of the thermionic tube is proportionate to the rate of interruption of the constant intensity light and the amplitude of the resulting signals is proportionate to the intensity of the continuous light.

12. In combination, a plurality of impedance devices, means for scanning a subject to produce a fluctuating beam of energy representative of the elemental areas of said subject, means for producing a fluctuating beam of energy of substantially constant frequency, means for causing certain of said impedance devices to respond to the beam of the scanning means, and means for causing certain others of said devices to respond to said beam of energy of constant frequency, said impedance devices being serially connected in circuit.

13. In combination, a plurality of light sensitive devices, means for scanning a subject to produce a fluctuating beam of energy representative of the elemental areas of said subject, means for producing a fluctuating beam of energy of substantially constant frequency, means for causing certain of said light sensitive devices to respond to the beam of the scanning means, and means for causing certain others of said devices to respond to said beam of energy of constant frequency, said light sensitive devices being serially connected in circuit.

14. In combination, a plurality of impedance devices, means for scanning a subject to produce a fluctuating beam of light representative of the elemental areas of said subject, means for producing a fluctuating beam of light of substantially constant frequency, means for causing certain of said impedance devices to respond to the beam, of the scanning means, and means for causing certain others of said devices to respond to said beam of light of constant frequency, said impedance devices being serially connected in circuit.

15. In combination, a plurality of light sensitive devices, means for scanning a subject to produce a fluctuating beam of light representative of the elemental areas of said subject, means for producing a fluctuating beam of light of substantially constant frequency, means for causing certain of said light sensitive devices to respond to the beam of the scanning means, and means for causing certain others of said devices to respond to said beam of light of constant frequency, said light sensitive devices being serially connected in circuit.

AUGUST KAROLUS. 

